From: Tim Gardner <tim.gardner@canonical.com>
Date: Tue, 24 Apr 2012 17:47:18 +0000 (-0600)
Subject: UBUNTU: SAUCE: Allow filtering of cpufreq drivers
X-Git-Url: http://git.alex.org.uk

UBUNTU: SAUCE: Allow filtering of cpufreq drivers

BugLink: http://bugs.launchpad.net/bugs/984288

Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Herton Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index cb0532b..57dfe00 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -570,6 +570,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			/proc/<pid>/coredump_filter.
 			See also Documentation/filesystems/proc.txt.
 
+	cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
+			to register. Example: cpufreq_driver=powernow-k8
+			Format: { none | STRING }
+
 	cpuidle.off=1	[CPU_IDLE]
 			disable the cpuidle sub-system
 
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 987a165..fe63d01 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1798,6 +1798,20 @@ static struct notifier_block __refdata cpufreq_cpu_notifier = {
  *               REGISTER / UNREGISTER CPUFREQ DRIVER                *
  *********************************************************************/
 
+static char cpufreq_driver_name[CPUFREQ_NAME_LEN];
+
+static int __init cpufreq_driver_setup(char *str)
+{
+	strlcpy(cpufreq_driver_name, str, CPUFREQ_NAME_LEN);
+	return 1;
+}
+
+/*
+ * Set this name to only allow one specific cpu freq driver, e.g.,
+ * cpufreq_driver=powernow-k8
+ */
+__setup("cpufreq_driver=", cpufreq_driver_setup);
+
 /**
  * cpufreq_register_driver - register a CPU Frequency driver
  * @driver_data: A struct cpufreq_driver containing the values#
@@ -1817,7 +1831,13 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	    ((!driver_data->setpolicy) && (!driver_data->target)))
 		return -EINVAL;
 
-	pr_debug("trying to register driver %s\n", driver_data->name);
+	pr_debug("trying to register driver %s, cpufreq_driver=%s\n",
+		driver_data->name, cpufreq_driver_name);
+
+	if (cpufreq_driver_name[0])
+		if (!driver_data->name ||
+			strcmp(cpufreq_driver_name, driver_data->name))
+				return -EINVAL;
 
 	if (driver_data->setpolicy)
 		driver_data->flags |= CPUFREQ_CONST_LOOPS;